Spinnerette for the production of hollow filaments



E. GRAFRIED 3,075,242 SPINNERETTE FOR THE PRODUCTION OF HOLLOW FILAMENTS Jan. 29, 1963 Filed May 23, 1960 iii. M

Q. M1 V/V/ ATTORNEYS 3,075,242 SPINNERETTE FtJR THE PRODUCTIQN F HGLLOW FILAMENTS Emil Graft-led, Grcssauheim (Main), Germany, assignmto W. C. Hcraeus, G.rn.b.H., Hanan (Main), Germany Filed May 23, 1960, Ser. No. 30,998 Claims priority, application Germany June 3, 1959 2 Claims. (Cl. 18-8) The present invention refers to spinnerettes for the production of hollow filaments, particularly from synthetic, organic materials of high molecular weight by extrusion of the molten material.

In the production of hollow filaments from rayon and cellulosic materials by extrusion into a solidifying bath, spinnercttes have been used in which the spinning orifices are provided with axially arranged wire cores in order to produce the hollow space within the filaments. It has been suggested that this type of spinnerettes with wires mounted in the orifices be used in the production of hollow filaments from synthetic material by extrusion of the molten mass. However, numerous attempts in this direction have demonstrated that spinnerettes provided with wire cores similar to that mentioned above can not be used for producing hollow filaments of thermoplastic materials.

It is known that synthetic, organic materials of high molecular weight such as polyarnides, polyvinyl compounds, polyethylene derivatives, polyterephthalic acid ester or the like are suitable for the production of filaments, and spinnerettes must be used which meet the specific requirements for extrusion from the molten mass. These requirements stem from the fact that the substances under consideration are extruded upon liquidation by heat. High melting temperatures and high pressures must be employed, as these materials can only be worked in the molten state and even then exhibit significant viscosity. Immediately upon leaving the spinning orifices, the filaments are stretched to a multiple of their original length, whereby great strength, particular in the case of this type of filament, is imparted to them; simultaneously, the cross section of this filament is reduced. When performing this stretching step, difficulties are encountered which make it impossible to use the known spinnerettes with wire cores for the purpose of producing synthetic, highmolecular organic filaments. it has been established that the filament walls are subject to pressure resulting from difference between the exterior pressure exerted by the atmosphere and the low pressure formed within the filament immediately upon leaving the spinning orifices and as a result of the stretching operation. Thus, the hollow space formed within the filament disappears immediately, and the attempted purpose of producing a regularly shaped hollow filament can not be achieved.

It is one object of the present invention to eliminate the shortcomings of spinncrettes with wire cores, in order to improve the production of hollow filaments from synthetic, organic materials of high molecular Weight. A further object of the invention is the provision of a spinncret'te which meets the requirements for successfully producing hollow filaments from a molten mass by extrusion. Other objects of the invention include the production of hollow threads having non-circular cross sections.

In accordance with one illustrative embodiment, a spinncrette is provided with an insert or core having a continuing cylindrical portion. The insert is fitted into a bore in the spinnerette plate, so that the continuing cylindrical portion and the wall of the bore form an endless slot defining a closed, generally circular, area in the outlet surface of the spinner-cite. When extruding a molten material of the type contemplated herein through the slot, a hollow filament is produced. A lateral bore ex- 3,075,242 Patented Jan. 29, 1953 "ice tends through the spinnerette and continues into the insert where it communicates with an axial bore in the insort and in the cylindrical continuing portion of the insert, the axial bore terminating in the closed area in the outlet surface defined by the slot. It will be apparent that these bores provide a channel connecting the interior of the hollow filament with the outer atmosphere during the extrusion and stretching step. Compression of the extruded filament is thereby prevented, since, when the filaments are stretched and pulled away from the spinnerette, the resulting low pressure operates to introduce air into the filament by suction. This results in the pro duction of a flawlessly shaped hollow filament.

In the foregoing paragraph, it is assumed that the channel form-ed by the bores provides a connection with the outer atmosphere, so that air is drawn into the hollow filament during the extrusion step. It will be apparent that any fluid introduced into the filament by suction will operate to equalize the pressure in the vicinity of the area defined by the closed slot, and therefore within the filament, with that at other points on the outlet surface of the spinnerette, which is the exterior pressure exerted upon the filament. In other words, and generally speaking, the bores provide a channel which communicates in any suitable manner with the volume or space into which the filaments are extruded. Any fluid present in this space will be drawn into the filament, as described above. Where the space into which the filaments are extruded is at atmospheric pressure, the bores may, of course, cornrnunicate with atmospheric pressure in any desired manner, and need not open directly into this space. Alternatively, suitable opposing pressure may be supplied through the bores in any known manner.

The spinnerette according to the invention leads to the production of hollow filaments having circular or noncircular cross section from synthetic, organic materials of high molecular weight and, in fact, has been found suitable for industrial purposes. As a result of the fact that air is introduced by suction through the lateral bores, the filament is not compressed during the stretching step; the inside diameter, as well as the outside diameter of the hollow filament remain substantially constant over the entire length thereof. Consequently, hollow threads produced by means of the spinnerette according to the invention particularly meet the requirements for heat insulalon and softness. These advantages are particularly significant since the invention provides a comparatively simple structure leading to the solution of the problem. It should be noted that much more intricate prior art constructions of spinnerettcs for the production of hollow filaments by extrusion of a molten mass did not accomplish the results achieved by the present invention.

The invention will be further illustrated by reference to the accompanying drawing in which a spinnerette is shown with only one spinning orifice, for the sake of simplification. However, for practical purposes, a spinnerctte of the type contemplated herein includes a plurality, generally, a great number, of identical spinning orifices.

in the drawing,

FlGURE 1 is a sectional view through a spinnerette according to the invention;

FlGURE 2 is a section view through the insert of FIG- URE 1;

FIGURE 3 is a bottom view of the insert of FIG- URE 2;

FIGURE 4 is a perspective view of the insert of FIG- URE 2 assembled with a spinnerette plate shown in section;

FIGURE 5 is a fragmentary sectional view of a spinnerctte for producing non-circular filaments; and

FIGURE 6 is a bottom view of FIGURE 5.

FIGURE 1 illustrates a spinnerette plate which is intended to be mounted in a conventional cup-shaped holder of any known type.

The spinnerette plate, designated by reference numeral 8 throughout all the figures, is provided with a bore including a first portion 10 having a comparatively large cross section and continuing over a conical portion 12 into a second short portion 14 of reduced diameter, which may be from about 1.50 mm. to about 0.20 mm. An insert 16 is fitted into this bore. The insert includes a cylindrical portion having two flattened side faces 18 and 2t and terminates in a cone 22 pointing toward the inlet surface in order to insure a uniform inflow of molten mass. The insert continues into a cylindrical portion 24 having a diameter smaller than that of the portion 14 of the bore in the spinnerette, to form an annular spinning orifice having the desired width of the wall of a hollow filament, as it is extruded and before stretching. The insert 16 is provided with an axial bore 28 which communicates with a radial bore 30. The outer diameter of the annular spinning orifice resulting from this arrangement is that of the bore 14, which may be about 1.25 mm., while the diameter of the axial bore 28 may be from about 1.00 mm. to about 0.19 mm. When the insert 16 is fitted into the spinnerette, as shown in FIGURES 1 and 4, the bore 30 meets a lateral bore 32 extending through the spinnerette 1. The combined bores 32, 30 and 28 form a continuing channel for drawing air from outside into a hollow filament when such filament is formed by extruding a molten mass through the annular spinning orifice defined by the short, cylindrical portion 14 of the bore through the spinnerette and the continuing insert portion 24.

During the spinning process, the molten material moves initially along the flattened sides 18 and of the upper portion of the insert 16. Then, it is passed through the mentioned annular space to form a hollow filament when it is extruded through the circular slot defined by the intersection of the annular space with the outlet surface. The formed filament is stretched until it reaches the desired length and the diminished cross section. Caused by the increase of volume due to the stretching operation, air is drawn by suction through the bores 32, 30 and 28, so that no low pressure is developed inside the filament; consequently, the filament is not compressed and the final product has the desired shape.

The additional advantage of hollow filaments with noncircular cross section may be achieved by providing grooves in the walls of the bore 14 which grooves extend longitudinally and inwardly from the edge with the outlet surface. At least one groove, preferably two or more, for example three grooves may be provided. Thereby, hollow filaments of synthetic, organic material of high molecular weight having a non-circular cross section are obtained. When more than four grooves are provided, a star-like configuration of the filament is obtained.

The number of grooves is not limited but should not be excessive, in order to avoid cancellation of the desired result which is obtained by departure from the circular form. The grooves may have any desired shape and good results have been obtained with rectangular or semicircular grooves.

An example of a spinnerette for producing non-circular hollow filaments is illustrated in FIGURES 5 and 6, in which identical parts are designated by the same reference numerals as in FIGURES 1 through 4.

In accordance with this embodiment, the cylindrical bore portion 14 is provided with grooves 34, which fact results in the formation of non-circular cross sections of the hollow filaments. By way of example, the grooves 34 are shown to have rectangular shape.

Evidently, the shape of the insert 16, as Well as that of the bores, may be modified within the scope of the invention. The insert may be provided with more than the two illustrated flattened sides 18 and 20, or with ribs as well,

in the number of four or six, for example. Similarly, instead of the cylindrical lateral bore 32 a conical bore may be provided for improving the convection of air. Furthermore, the bores need not be arranged in a right angle to the direction of flow of the molten mass but they may be arranged in an angle which is different from a right angle, for example in an obtuse angle.

The spinnerette according to the invention may be made from metals and alloys known in the art, such as precious metals and alloys thereof; suitably, stainless steel or platinum group metals may be used. Furthermore, the insert may be formed from a material which is different from that of the spinnerette; however, in most instances it is advantageous to use the same metal, in order to prevent loosening of the insert, which may result from a difference in thermal expansion coefficients.

What is claimed is:

l. A spinnerette comprising a heavy bottom plate having inlet and outlet surfaces and at least one bore connecting one with the other, said bore forming an opening in said outlet surface, an insert fitted axially in said bore, said insert having a cylindrical end portion of smaller diameter coaxially maintained within said opening to form a spinning orifice in the outlet surface having the shape of an endless slot defining a closed area, the remainder of said insert having at least one longitudinal portion removed to form a connecting channel from said inlet surface to said endless slot, and a sequence of bores for admitting air through said bottom plate and into said closed area, said sequence of bores including an axial bore through said insert having a first end terminating in said closed area, the second end terminating within said insert, a laterally extending bore through said insert communicating with said second end, and a continuing bore through said bottom plate for connecting said laterally extending bore with a location on the surface of the bottom plate outside said closed area.

2. A spinnerette comprising a heavy bottom plate having inlet and outlet surfaces and at least one bore connecting one with the other, said bore including an essentially cylindrical main portion and a short cylindrical outlet portion of restricted diameter, an insert having a cylindrical main portion fitted into the main portion of said bore having at least one longitudinal flattened area to form a passageway between itself and the bore wall and terminating in a cone pointing toward and terminating adjacent said inlet surface, the insert having a cylindrieal continuing end portion of restricted diameter protruding into said cylindrical outlet portion of said bore, the diameter of said outlet portion of said bore exceeding that of the cylindrical insert end portion to form a spinning orifice in the outlet surface having the shape of a circular slot enclosing a circular area, and a sequence of bores for admitting air through said bottom plate and through said insert into said circular area, said sequence of bores including a first axial bore throuph said cylindrical insert end portion having a first end terminating in said enclosed circular area, the second end terminating within said main portion of said insert, a second lateral bore extending substantially perpendicularly with respect to and communicating with said first bore, and a third bore through the bottom plate communicating with said second bore, all three bores together forming one continuing pressure-resistant channel for connecting said circular area with a location on the outer surface of the bottom plate outside said area to permit the access of air to the interior of a hollow filament formed by extruding plastic material through said circular slot.

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) UNITED STATES PATENTS Davidson et a1. Oct. 19, 1926 Fisch June 29, 1954 FOREIGN PATENTS France Nov. 2, 1942 6 France Nov. 29, 1950 Germany Sept. 29. 1918 Germany Dec. 31, 1958 Italy Dec. 4, 1943 Switzerland June 11, 1897 

1. A SPINNERETTE COMPRISING A HEAVY BOTTOM PLATE HAVING INLET AND OUTLET SURFACES AND AT LEAST ONE BORE CONNECTING ONE WITH THE OTHER, SAID BORE FORMING AN OPENING IN SAID OUTLET SURFACE, AN INSERT FITTED AXIALLY IN SAID BORE, SAID INSERT HAVING A CYLINDRICAL END PORTION OF SMALLER DIAMETER COAXIALLY MAINTAINED WITHIN SAID OPENING TO FORM A SPINNING ORIFICE IN THE OUTLET SURFACE HAVING THE SHAPE OF AN ENDLESS SLOT DEFINING A CLOSED AREA, THE REMAINDER OF SAID INSERT HAVING AT LEAST ONE LONGITUDINAL PORTION REMOVED TO FORM A CONNECTING CHANNEL FROM SAID INLET SURFACE TO SAID ENDLESS SLOT, AND A SEQUENCE OF BORES FOR ADMITTING AIR THROUGH SAID BOTTOM PLATE AND INTO SAID CLOSED AREA, SAID SEQUENCE OF BORES INCLUDING AN AXIAL BORE THROUGH SAID INSERT HAVING A FIRST END TERMINATING IN SAID CLOSED AREA, THE SECOND END TERMINATING WITHIN SAID INSERT, A LATERALLY EXTENDING BORE THROUGH SAID INSERT COMMUNICATING WITH SAID SECOND END, AND A CONTINUING BORE THROUGH SAID BOTTOM PLATE FOR CONNECTING SAID LATERALLY EXTENDING BORE WITH A LOCATION ON THE SURFACE OF THE BOTTOM PLATE OUTSIDE SAID CLOSED AREA. 